<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>字体大小</title>
    <style>
         h2{
            font-size: 16px;
        }
        body{
            font-size: 20px;
        }
       
    </style>
</head>
<body>
    <h2>一个小标题，标题搞特殊</h2>
    <h4>又一个小标题，又搞特殊</h4>
    <p>p标签里边的一句话</p>
</body>
</html>